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Abstract:

A process for making microcapsules comprising i) forming a solution of a
cross-linker in a liquid; ii) forming a slurry of a surface-modified
particulate inorganic material in an aqueous medium; and iii) dispersing
the solution of step i) in the slurry of step ii) and causing or allowing
the cross-linker to react with the surface-modified particulate inorganic
material so as to form a cross-linked microcapsule wall.

Claims:

1. A process for making microcapsules comprising; i) forming a solution
of a cross-linker in a liquid; ii) forming a slurry of a surface-modified
particulate inorganic material in an aqueous medium; and iii) dispersing
the solution in the slurry and causing or allowing the cross-linker to
react with the surface-modified particulate inorganic material so as to
form a cross-linked microcapsule wall.

2. A process as claimed in claim 1 in which the liquid is substantially
insoluble in water.

3. A process as claimed in claim 2 in which the liquid has a solubility
in water at 20.degree. C. of less than 10 g/l.

4. A process as claimed in claim 1 in which the liquid comprises an
active material which is an agrochemical.

5. A process as claimed in claim 4 in which the active material is an
insecticide.

6. A process as claimed in claim 5 in which the insecticide is a
pyrethroid.

7. A process as claimed in claim 6 in which the pyrethroid is
lambda-cyhalothrin.

8. A process as claimed in claim 1 in which the particulate inorganic
material comprises an oxy-compound of at least one of calcium, magnesium,
aluminium and silicon; or a derivative of such a compound.

9. A process as claimed in claim 8 in which the particulate inorganic
material is or is derived from silica, a silicate, marble, a clay or
talc.

10. A process as claimed in claim 9 in which the particulate inorganic
material is a clay.

12. A process as claimed in claim 1 in which the particulate inorganic
material has a median diameter (d50) less than or equal to 10 μm.

13. A process as claimed in claim 1 in which the particulate inorganic
material has a particle size distribution where at least about 90% of the
particles by weight are smaller than about 2 μm.

14. A process as claimed in claim 1 in which the particulate inorganic
material has a particle size distribution where at least about 90% of the
particles by weight are less than about 2 μm, at least about 90% of
the particles by weight are less than about 1 μm, and at least about
75% of the particles by weight are less than about 0.25 μm.

15. A process as claimed in claim 1 in which the particulate inorganic
material particle surface has been modified so as to have reactive groups
by reaction with a chemical of the general structure X--Y--Z, in which X
is a chemical moiety with a high affinity for the particle surface; Z is
a reactive chemical moiety; and Y is a chemical moiety that links X and Z
together.

16. A process as claimed in claim 15 in which X is an alkoxy-silane
group.

17. A process as claimed in claim 15 in which Y is a C2-6 alkylene
chain.

18. A process as claimed in claim 15 in which Z is an amine group.

19. A process as claimed in claim 1 in which the surface-modified
particulate inorganic material is clay which has been surface-modified
with an amino-silane.

20. A process as claimed in claim 1 in which the cross-linker is a
polyisocyanate.

21. A process as claimed in claim 1 where the cross-linked microcapsule
wall is modified through addition of an extra cross-linking molecule.

22. A process as claimed in claim 1 in which the particulate inorganic
material is natural.

23. A process as claimed in claim 1 in which the particulate inorganic
material is synthetic.

24. A microcapsule comprising an encapsulated material surrounded by a
wall, characterised in that the wall comprises a particulate inorganic
material that has been surface-modified and cross-linked.

25. A microcapsule as claimed in claim 24 which contains an active
ingredient encapsulated within the core of the microcapsule.

26. A microcapsule as claimed in claim 25 where the active ingredient is
an agrochemical.

27. (canceled)

28. (canceled)

29. (canceled)

Description:

[0001] The present invention relates to a novel process for making
microcapsules and to microcapsules made by the process. It also relates
to a process for the use of the microcapsules.

[0002] Microcapsules are small capsules which comprise a wall which
surrounds an encapsulated material, generally a liquid. They may be used
for protecting the encapsulated material from the external environment,
for example from degradation by air or light (especially u.v. radiation).
They may also be used to isolate hazardous materials within the
microcapsule to make them safer to handle or use. Microcapsules are known
to be used for agrochemicals, particularly insecticides such as lambda
cyhalothrin, to protect them from degradation by UV light and to provide
controlled release following application.

[0003] Certain known microcapsules are made by interfacial polymerisation.
In such a process a solution is first formed of a first monomer, such as
a polyisocyanate, in a water-insoluble liquid to be encapsulated. The
solution may also contain a biologically active ingredient. This solution
is then dispersed in water together with surfactants to form an emulsion.
A suitable second monomer such as a polyamine is added to the water and
this reacts with the first monomer at the surface of the emulsion
droplets to make a cross-linked polymer, in this example a polyurea,
which forms a microcapsule wall around the droplets. Known first and
second monomers also include polyisocyanate and polyol to make a
polyurethane wall, polyfunctional acid halide and polyamine to make a
polyamide wall and polyfunctional acid halide and polyol to make a
polyester wall.

[0004] There are disadvantages of these types of microcapsules. Polymeric
capsule walls of this known type provide poor protection for the contents
from UV light. Also, the surfactant which is used to form the emulsion
may lead to a problem when later handling the dispersion of microcapsules
because it may cause foaming.

[0005] In one known approach, photoprotectants form part or all of the
microcapsule wall materials and thus provide a shield for the capsule,
thereby protecting any photosensitive active ingredient that is present
within the capsules. For example CA2133779 shows that lignosulphonates
and the like can be used in combination with a protein such as a high
bloom gelatin to form a capsule wall that improves the resistance of
agriculturally active substances, such as pesticides, to u.v. light
degradation. The capsule wall formed by the interaction of these
components is durable and has a u.v. protectant as an integral part of
its structure.

[0006] Moy describes in EP539142A1 the use of colloidal inorganic
particles, particularly those of silica and zirconium dioxide, to make
microcapsules by coacervation or by interfacial polymerisation methods.
The process involves the formation of so called Pickering emulsions and
the thermoset microcapsule wall comprises the inorganic particles. Moy
does not contemplate the use of surface-modified particles, not the use
of cross-linkers to form the capsule wall.

[0007] Co-pending international application PCT/GB2007/003374 is concerned
with light protecting particles which are chemically bonded to the
microcapsule wall but does not contemplate microcapsule walls formed from
light protecting particles themselves.

[0008] The present invention provides an aqueous dispersion of
microcapsules having a cross-linked particulate inorganic wall in an
aqueous medium. In a further aspect, these microcapsules may be further
modified by adding, to the aqueous medium, a material which will further
react with any remaining cross-linker. For example, when the cross-linker
is a polyisocyanate, a polyamine such as diethylentriamine may be added.
This causes further cross-linking and polymer formation at the
microcapsule particulate inorganic wall and may be used to modify the
durability of the capsules or permeability of the capsule walls to give,
for example, a longer release time under given conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention will be better understood with reference to the
detailed description when considered in conjunction with non-limiting
examples and the accompanying drawings.

[0010] FIG. 1 is a light microscope image of the clay dispersion of
Example 1.

[0011] FIG. 2 is a light microscope image of the Pickering emulsion of
Example 2.

[0012] FIG. 2a is a light microscope image showing that the emulsion
droplets collapse on drying in air on a glass slide.

[0013] FIG. 2b is a light microscope image showing the affect of addition
of 5% by weight Synperonic® NP8 to a Pickering emulsion.

[0014] FIG. 3 is a light microscope image of the microcapsules of Example
3.

[0015] FIG. 3a shows a stable microcapsule dispersion of FIG. 3.

[0016]FIG. 3b shows the microcapsules of FIG. 3 after the addition of
Synperonic® NP8.

[0017]FIG. 4 is a Scanning Electron Microscope image of the capsules of
Example 4.

[0018] FIG. 5 is a light microscope image of the capsules of Example 5.

[0028] FIG. 9 shows the results of a comparative study of capsules
prepared according to Examples 11a and 11b.

[0029] FIG. 10 shows the release rate of dimethylphthalate [DMP] into
water of capsules prepared according to Example 12.

[0030] FIG. 11 is a light microscope image of capsules prepared according
to Example 13 in their original dispersion.

[0031] FIG. 12 is a light microscope image of capsules prepared according
to Example 13 in a dispersion formed from a redispersion after drydown.

[0032] The present invention relates to a new process for making
microcapsules which does not require surfactant and which provides
microcapsules having an increased, relatively high level of protection
from u.v. light for the contents; the present invention involves the use
of surface-modified particulate inorganic material to form microcapsule
walls where a cross-linker is used to react with a reactive functional
group on the surface-modified material such that each microcapsule wall
is a cross-linked wall. The present invention does also allow surfactants
to be used in the same formulation as a Pickering emulsion based system.
Pickering emulsions are often destabilized by surfactants but in the
present invention, cross-linking of the interfacial particles prevents
this from occurring and surfactants may be safely added to the system
once the interfacial cross-linking has occurred. Therefore, suitably,
adjuvants may be built-in to microcapsule compositions of the present
invention.

[0033] Microcapsules of the present invention are suitable for controlled
release applications (for instance, controlled release of an active
ingredient from within the core of the microcapsules). The controlled
release rate may be tailored through the present invention.

[0034] Another aspect of the present invention is that the cross-linked
systems may be easily modified through addition of an extra cross-linking
molecule (for example, a water dispersible isocyanate or polyfunctional
cross-linker, such as diethylenetriamine [DETA]) to the outer (external
or continuous) phase of the dispersion such that the release rate of any
active ingredient from within the core of the capsule may be varied to
give a desired release rate profile. The opportunity to use extra
cross-linking molecules means that it is possible to strengthen an
existing layer in a single-layered capsule or to form multi-layered
capsules.

[0035] The microcapsules of the present invention may be made by a process
comprising:

i) forming a solution of a cross-linker in a liquid; ii) forming a slurry
of a surface-modified particulate inorganic material in an aqueous
medium; iii) dispersing the solution of step i) into the slurry of step
ii) to form a Pickering emulsion and causing or allowing the cross-linker
to react with a reactive functional group on the surface-modified
particulate inorganic material so as to form a cross-linked microcapsule
wall.

[0036] Steps (i) and (ii) may be carried out in any order.

[0037] A slurry is a suspension of a solid in a liquid; in this invention,
the slurry formed in step is a suspension of cross-linkable,
surface-modified inorganic particles in an aqueous-based medium. It has
been found that it is possible to disperse the solution of step i) into
the slurry of step ii) without using additional surfactants. This is
because the particles of surface-modified inorganic material tend to
accumulate at the interface between the solution droplets and the aqueous
continuous phase and reduce the corresponding surface energy. This effect
is known as a `Pickering Emulsion`. The use of this combination of a
Pickering Emulsion with a cross-linkable particulate inorganic material
and a cross-linker allows for a particularly simplified process.

[0038] The liquid used in step i) comprises material to be encapsulated.
In one embodiment, the liquid comprises an active ingredient which is to
be encapsulated, optionally together with a solvent, particularly if at
room temperature the active ingredient is a solid, or of high viscosity.
Therefore, when present, the active ingredient may be the liquid, a part
of the liquid, dissolved in the liquid, dispersed in the liquid or is a
solid complex of an agrochemical with a molecular complexing agent and is
dispersed in the liquid. The liquid is suitably substantially insoluble
in water, more suitably it has a solubility in water at 20° C. of
less than 10 g/l and most suitably less than 5 g/l. The liquid must
dissolve the cross-linker so as to form a solution.

[0039] Any active ingredient encapsulated within the core of the
microcapsules is suitably less than 10% by weight soluble in water and
more suitably less than 1% by weight soluble in water; and most suitably
less than 0.1% by weight soluble in water.

[0040] A wide range of active materials (active ingredients) may be
encapsulated including inks, flavours, cosmetics, perfumes, sunscreens,
fragrances, adhesives, sealants, phase change materials, biocides,
oilfield chemicals (including corrosion and scale inhibitors), flame
retardants, food additives (including vitamins, ingredients, probiotics
and antioxidants), active agents that may be included in detergent,
fabric softeners and other household products (such as bleaches, enzymes
and surfactants), active agents that may be included in textiles (such as
insect repellents, antimicrobial agents, skin softeners and medically
active compounds), active agents that may be included in coatings (such
as fire retardant, flame retardant, antifouling, antibacterial, biocidal,
scratch resistant and abrasion resistant compounds) and biologically
active compounds (such as pharmaceuticals and agrochemicals). Suitably
the active material is an agrochemical such as a herbicide, fungicide or
insecticide. Many such agrochemicals are known and are described in The
Pesticide Manual 14th edition published by the British Crop Protection
Council in 2006. The invention is also suitable for encapsulating a solid
complex of an agrochemical with a molecular complexing agent including,
for example, a complex of 1-MCP and α-cyclodextrin. The invention
is most useful for agrochemicals that are subject to degradation when
exposed to sunlight, in particular pyrethroid insecticides such
deltamethrin, tralomethrin, cyfluthrin, alphamethrin, zeta-cypermethrin,
fenvalerate, esfenvalerate, acrinathrin, allethrin, bifenthrin,
bioallethrin, bioresmethrin, cycloprothrin, beta-cyfluthrin, cyhalothrin,
beta-cypermethrin, cyphenothrin, empenthrin, etofenprox, fenpropathrin,
flucythrinate, tau-fluvalinate, phenothrin, prallethrin, resmethrin,
tefluthrin, tetramethrin, and lambda-cyhalothrin; suitably
lambda-cyhalothrin.

[0041] Suitably, microcapsules of the present invention may be used in
wall-boards or plasterboards in buildings, and may be used in improving
cement compositions and processes for making cementitious materials.

[0042] The active ingredient is suitably a pharmaceutical compound or an
agrochemical; more suitably it is an agrochemical.

[0043] Suitably, the agrochemical is a fungicide, insecticide, herbicide
or growth regulator, used for controlling or combating pests such as
fungi, insects and weeds or for controlling the growth of useful plants.
The agrochemical may also be used in non-agricultural situations [for
example public health and professional product purposes, such as termite
barriers, mosquito nets and wall-boards].

[0044] Further suitable applications include, without limitation:

[0045] Sustained release or controlled release usages, for example:
pharma, for example acid resistant capsules (oral delivery past low pH in
the stomach), protection of labile actives, pseudo-zero order release
through capsule wall and Ostwald-ripening resistant emulsion
formulations; cosmetics; perfumes, for example slowing down evaporation
of top-notes or sustained release and minimising overpowering odours;
capsules having affinity for cellulose and trapped on textile surface
during laundering; flavours, for example light stabilised to prevent
oxidation; self-healing coatings, for example capsule bursts to release a
resin that repairs damage; carbonless copy paper; novel, double taste and
texture food, for example capsule which dissolves in the mouth and
releases a new taste; pressure sensitive adhesives; sealants; nutrition
(for example increased bioavailability of complex molecules and
protection of sensitive molecules such as vitamins, probiotics and other
food additives); toner inks with photosensitivity or thermal sensitivity;
textile coatings, for example, for improving permeability properties;
antifouling coatings; surface protective coatings, for example, for
improving scratch or abrasion resistance; and construction materials, for
example wall-boards, plasterboards and cements. Example of capsules that
are dried out, include, for example, various mineral blends to form a
ceramic upon calcination; low density fillers for polymers or paints;
insulating materials; low density proppants; light reinforcing particles,
for example for wood-fibre composites; recyclable pigments, for example
low density allowing easy flotation separation; and energy buffers, for
example use in a void in spheres to provide a `crash barrier` with
adsorption of energy. Capsules of the present invention may be of novel
size or shape, for example: creation of plate or rod shape capsules; and
use of metallic particles resulting in conductive capsules, or having a
metallic nature, for example plasmon absorbance.

[0046] A solution suitable for use in step i) may be made by stirring a
liquid and a cross-linker together. Heating and mechanical agitation may
be used to aid or accelerate dissolution of the cross-linker. Similar
techniques may be used to mix or dissolve an active ingredient with any
solvent that is optionally included.

[0048] In one aspect of the invention, the particulate inorganic material
is kaolin clay. Kaolin clay is also referred to as china clay or hydrous
kaolin, and is predominantly mineral kaolinite
(Al2Si2O5(OH)4), a hydrous aluminium silicate (or
aluminosilicate).

[0049] The particulate inorganic material suitably has a particle size
distribution wherein the median diameter (d50) is less than or equal
to 10 μm, as measured by determining the sedimentation speeds of the
dispersed particles of the particulate material under test through a
standard dilute aqueous suspension using a SEDIGRAPH®, for example
SEDIGRAPH® 5100, obtained from Micromeritics Corporation, USA.
Suitably, the particulate inorganic material has a d50 less than or
equal to 5 μm. More suitably, the particulate inorganic material has a
d50 less than or equal to 2 μm. Yet more suitably, the
particulate inorganic material has a d50 less than or equal to 1
μm. In increasing suitability, the particulate inorganic material has
a d50 less than or equal to 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3
μm. In other aspects, the particulate inorganic material has a
d50 less than or equal to 0.2 μm, for example less than or equal
to 0.15 μm or less than or equal to 0.12 μm or less than or equal
to 0.1 μm.

[0050] In one aspect, at least about 90% of the particles of the
particulate inorganic material by weight are smaller than about 2 μm,
for example at least about 95% or 98% are smaller than about 2 μm.
Suitably, at least about 90% of the particles by weight are smaller than
about 1 μm, for example at least about 95% or 98% are smaller than
about 1 μm. More suitably, at least about 75% of the particles by
weight are smaller than about 0.25 μm, for example at least about 80%
or 82% are smaller than about 0.25 μm. In another aspect, the
particulate inorganic material has a particle size distribution of (i) at
least about 90% of the particles by weight less than about 2 μm, for
example at least about 95% or 98%; (ii) at least about 90% of the
particles by weight are less than about 1 μm, for example at least
about 95% or 98%; and (iii) at least about 75% of the particles by weight
are less than about 0.25 μm, for example at least about 80% or 82%;
and particulate inorganic material of such particle size distributions
may also have d50 values at the smaller end of the range, for
example at least about 98% of the particulate inorganic material by
weight is smaller than about 2 μm, at least about 98% is smaller than
about 1 μm, at least about 82% is smaller than about 0.25 μm, and
the d50 value of the particulate inorganic material is less than or
equal to 0.12 μm.

[0051] For finer particulate inorganic material (for example having a
d50 less than or equal to 2 μm), the material may be derived
through classification, including methods such as gravity sedimentation
or elutriation, use of any type of hydrocyclone apparatus or, for
example, a solid bowl decanter centrifuge or a, disc nozzle centrifuge.
The classified particulate inorganic material may be dewatered in one of
the ways known in the art, for example filtration (including filter
press), centrifugation or evaporation. The classified, dewatered material
may then be thermally dried (for example, by spray drying).

[0052] Surface-modified means that the inorganic particle surface has been
(chemically) modified so as to have cross-linkable, reactive functional
groups. The surface of the particles may be modified using modifying
agents selected from a wide variety of chemicals, with the general
structure X--Y--Z, in which X is a chemical moiety with a high affinity
for the particle surface; Z is a (reactive) chemical moiety with a
desired functionality; and Y is a chemical moiety that links X and Z
together. The term `high affinity` relates to chemical moieties that are
either chemically bonded or strongly physisorbed to the particle surface;
suitably they are chemically bonded.

[0053] X may be, for example, an alkoxy-silane group such as
tri-ethoxysilane or tri-methoxysilane, which is particularly useful when
the particles have silanol (SiOH) groups on their surface. X may also be,
for example, an acid group (such as a carboxylic or an acrylic acid
group) which is particularly useful when the particles have basic groups
on their surface.

[0054] Y may be any chemical group that links X and Z together, for
example a polyamide, a polyester or an alkylene chain; more suitably it
is an alkylene chain; and even more suitably it is a C2-6 alkylene
chain, such as ethylene or propylene.

[0055] Reactive groups Z may be selected from any groups, preferably
different from Y, which can be used to react with a cross-linker so as to
cross-link the surface modified particulate inorganic material. Examples
of Z are epoxy groups, carboxylic groups, unsaturated groups such as
acrylic or vinyl groups and, suitably, amine groups.

[0056] Suitable examples of surface modification rely on reaction of clay
with aminosilanes, such as aminopropyltrimethoxysilane. The silane groups
react with the clay so as to give free amine groups attached to the clay
surface. An extensive range of silanes exists, able to modify surfaces
with functionality appropriate for use in a range of polymer systems.

[0057] The reactive groups Z are reacted with a cross-linker so as to form
a capsule wall. Cross-linkers are compounds that have at least two
reactive groups that will react with the reactive groups on the
surface-modified particles. Examples of cross-linkers that may be used to
react with amine groups on a clay particle are polyisocyanates.
Polyisocyanates provide a well-known class of cross-linker and include
diisocyanates (such as toluene diisocyanate, hexamethylene diisocyanate
and isophorone diisocyanate); isocyanates with, on average, more than two
isocyanate groups (such as polymethylenepolyphenylene isocyanate); and
many others including prepolymers of diisocyanates such as their reaction
products with trimethylol propane and other simple polyols sold as
Desmodur® resins from Bayer.

[0058] Examples of cross-linkers that may be used to react with epoxy
groups; with carboxylic groups; or with unsaturated groups such as
acrylic or vinyl groups will be familiar to the person skilled in the
art.

[0059] In one embodiment, clay is reacted with a suitable modifying agent,
in the range of from 0.1 to 30% of the modifying molecule based on the
weight of the clay (suitably in the range of from 0.1 to 20% and most
suitably the range is from 0.1 to 10% by weight).

[0060] The aqueous medium suitable for use in step ii) mostly comprises
water, for example by weight it is more than 80% water; and suitably more
than 90% water. Optionally, the aqueous medium also comprises water
miscible solvents, antifreeze agents or additional surfactants, although
as mentioned above, these are not necessary. It has been found that
surfactants may interfere with the formation of a Pickering emulsion and
so it is preferred not to include surfactants at this stage.

[0061] A slurry suitable for use in step ii) may be made by agitating the
particulate inorganic material in the aqueous medium using a mechanical
stirrer (for example a Rotor/stator, Ystral® or Ultra Turrax®) or
by ultrasonic agitation. Suitably the slurry is agitated until the
solution is added to it and the dispersion step is carried out.

[0062] In step iii), the solution may be dispersed in the slurry by
conventional means such as ultrasonic dispersers or, suitably, high speed
mechanical dispersers such as a Rotor/stator mixer, Ystral® or Ultra
Turrax®. The dispersion process is carried out for a period between 30
seconds and 20 minutes.

[0063] The dispersion step iii) results in a dispersion of the solution in
the slurry which is stabilised as a Pickering emulsion by the
surface-modified particulate inorganic material. This emulsion comprises
droplets of the solution which are surrounded by and stabilised by the
particles of the inorganic material. The cross-linker in the solution
reacts with the reactive functional groups on the particulate inorganic
material so as to form a cross-linked microcapsule wall. This reaction
can be carried out simply by allowing the dispersion to stand at ambient
temperature. Alternatively, the dispersion may be heated. The amount of
time and the optimum temperature may be established by routine
experimentation. Typically, when the particulate inorganic material is
surface-modified so as to have amine groups on its surface and the
cross-linker is a polyisocyanate, stirring the dispersion at between 15
and 25° C. for an hour is sufficient to complete the reaction.

[0064] The weight ratio of inorganic particle to solution phase will be
from 1:0.1 to 1:40; suitably from 1:1 to 1:20.

[0065] The cross-linker may be used at a rate of from 0.1 to 30% w/w of
the oil phase, more suitably from 0.5 to 20% and most suitably from 1 to
10%.

[0066] The reaction may be controlled by pH, temperature, addition of an
electrolyte or by the use of a catalyst.

[0067] The process results in a dispersion of microcapsules in an aqueous
medium. These microcapsules may be further modified by the addition to
the aqueous medium of a material which will further react with any
remaining cross-linker. For example, when the cross-linker is a
polyisocyanate, a polyamine such as diethylentriamine may be added. This
causes further cross-linking and polymer formation at the microcapsule
wall and may be used to modify the durability of the capsules or
permeability of the capsule walls to give, for example, a longer release
time under given conditions.

[0068] The microcapsules may be isolated by drying, for example spray
drying, to form a powder or may be used as the dispersion in the aqueous
medium. When the microcapsules are isolated, they may be used dry or they
may be redispersed in water before use.

[0069] The microcapsules made according to this process are new. According
to the present invention there is provided a microcapsule comprising an
encapsulated material surrounded by a wall, characterised in that the
wall comprises a particulate inorganic material that has been
surface-modified and cross-linked.

[0070] The invention is illustrated by the following Examples. The
particulate inorganic material used in the Examples is a tabular (so
called "blocky", flat or plate-like shape) ultrafine kaolin, having a
d50 of 0.12 μm and a particle size distribution with at least 98%
of the particles by weight smaller than 1 μm and at least 82% smaller
than 0.25 μm.

[0071] In these Examples, D[4,3] is the volume mean diameter of the
relevant particles, capsules or droplets as obtained by laser light
scattering of a diluted sample in a Malvern Mastersizer® 2000.

EXAMPLE 1

[0072] This Example illustrates the preparation of a surface-modified clay
dispersion. Clay particles (ultrafine tabular Kaolin sourced in the USA,
obtained from Imerys) were surface modified by the addition of 1.6% by
weight aminopropyltriethoxysilane. The surface-modified particles were
then added to water and dispersed with an Ultrasonic Probe (Sonics and
Materials, Vibra Cell®, with microtip--hereinafter referred to as an
Ultrasonic Probe) operated under the following conditions: 50% Duty
cycle; Output Control 4; for 6 minutes. The composition is given in Table
1.

[0074] FIG. 1 is a light microscope image of the clay dispersion of
Example 1.

EXAMPLE 2

[0075] This Example illustrates the preparation of a simple Pickering
emulsion.

[0076] Initially, Solvesso® 200ND (aromatic oil from Exxon) was
dispersed dropwise into the continuous phase of a modified Kaolin
dispersion prepared according to Example 1, under high shear mixing with
an Ystral® high shear mixer (type X1020) with a two-pronged T10 head
(hereinafter referred to as an Ystral® high shear mixer) operated at
about 5000 rpm. The concentrations of the ingredients used are given in
Table 2.

[0077] Subsequent high shear mixing by the Ystral® high shear mixer
operated at about 20000 rpm for 2 minutes produced an oil in water [O/W]
Pickering emulsion.

[0079] FIG. 2 is a light microscope image of the Pickering emulsion of
Example 2.

[0080] FIG. 2a is a light microscope image showing that the emulsion
droplets collapse on drying in air on a glass slide; the emulsion has
broken.

[0081] FIG. 2b shows that the addition of 5% by weight Synperonic® NP8
to the Pickering emulsion causes the emulsion to break after 4 days, as
shown by light microscopy.

EXAMPLE 3

[0082] This Example illustrates the preparation of a single-layered
capsule suspension. A solution of 5% w/w Suprasec® 5025 (polymethylene
polyphenylene isocyanate; PMPI) was prepared in Solvesso® 200ND.
Meanwhile, extra water was added to a surface-modified Kaolin dispersion
prepared according to Example 1 and then to this dispersion, the
Solvesso® 200ND plus Suprasec® 5025 solution was added dropwise
with mixing by a Ystral® high shear mixer operated at about 5000 rpm.
The concentrations of the ingredients used are given in Table 3.

[0083] Subsequently, an oil in water [O/W] emulsion was prepared, by high
shear mixing with the Ystral® high shear mixer at about 20000 rpm for
2 minutes, which then developed into a microcapsule system as a
cross-linking reaction took place.

[0085] FIG. 3 is a light microscope image of the microcapsules of Example
3. After ageing for at least 1 day, the microcapsules did not collapse
upon drying on a glass microscope slide [see light microscope image, FIG.
3a, which shows a stable microcapsule dispersion] demonstrating that the
wall had increased mechanical strength compared to the simple emulsion of
Example 2. Addition of 5% w/w Synperonic® NP8 did not cause the
emulsion to break after a period of 1 week [see light microscope image,
FIG. 3b, taken after the addition of Synperonic® NP8 and showing
unbroken capsule dispersion] demonstrating that cross-linking anchored
the surface-modified clay at the interface such that it was not displaced
by the surfactant. Pickering emulsions are usually incompatible with
surfactants (as shown in FIG. 2b); cross-linking the particles allows
them to be used with surfactants.

EXAMPLE 4

[0086] This Example illustrates the preparation of a two-layered capsule
suspension. Bayhydur® 3100 [polyisocyanate based on hexamethylene
diisocyanate modified with a polyether chain for water dispersibilty
(from Bayer)] was dispersed in water by shaking and then the resultant
Bayhydur® 3100 solution was added dropwise to a single-layered capsule
suspension prepared according to Example 3 with mixing from a Ystral®
high shear mixer at about 5000 rpm throughout the dropwise addition.

[0087] The resultant capsule suspension was then mixed with the Ystral®
high shear mixer at about 20000 rpm for 2 minutes. The composition is
given in Table 4.

[0088] Result: The capsules remained intact during dry down and
examination in a Scanning Electron Microscope, see FIG. 4, showing they
had good mechanical strength. The Bayhydur® 3100 can be seen as
spheres attached to the outside of the capsule walls. The capsules were
sufficiently strong for them to survive high shear mixing at 20000 rpm
for 2 minutes with an Ystral® high shear mixer.

EXAMPLE 5

[0089] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine; it is similar to Example 3
but it has a second cross-linker. A 25% w/w solution of
diethylenetriamine (DETA) was prepared in water and then this aqueous
DETA solution was added dropwise to a single-layered capsule suspension
prepared according to Example 3 with mixing from an Ystral® high shear
mixer at about 5000 rpm. This capsule suspension was then mixed by the
Ystral® high shear mixer at about 20000 rpm for 2 minutes. The
composition is given in Table 5.

[0091] FIG. 5 is a light microscope image of the capsules of Example 5.

[0092] The capsules remained intact during either dry-down on a glass
microscope slide or dry-down plus examination in a scanning electron
microscope [SEM], demonstrating that they have good mechanical strength.
The fact that there is no capsule collapse under SEM conditions
demonstrates that the presence of the second cross-linker has enhanced
the mechanical strength of the capsules compared to these of Example 3.
The capsules were sufficiently strong for them to survive high shear
mixing at 20000 rpm for 2 minutes with the Ystral® high shear mixer.

[0095] This Example compares the release rate of non-cross-linked and
cross-linked Pickering emulsions, compared to a polymer-stabilized
emulsion.

EXAMPLE 6a

[0096] This Example illustrates preparation of a simple Pickering
emulsion.

[0097] A 50% by weight solution of dimethylphthalate in Solvesso®200ND
was dispersed dropwise into a surface-modified Kaolin dispersion prepared
according to Example 1, under high shear mixing with an Ystral® high
shear mixer at about 5000 rpm throughout the dropwise addition and an O/W
emulsion was then prepared by high shear mixing with the Ystral® high
shear mixer at about 20000 rpm for 2 minutes. The composition is given in
Table 6a.

[0100] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing dimethylphthalate
prepared by an Ultrasonic process. A 10% w/w Suprasec® 5025, 45% w/w
dimethyl phthalate and 45% w/w Solvesso®200ND solution was dispersed
dropwise into a surface-modified kaolin dispersion prepared according to
Example 1, under agitation with an Ultrasonic Probe;

and then an O/W emulsion was prepared by high shear mixing with the
Ultrasonic Probe for 2 minutes, under the following conditions: 50% Duty
cycle, Output Control 4. To this emulsion, a 25% w/w diethylenetriamine
solution was added under mixing with the Ultrasonic Probe. The full
composition is given in Table 6b.

[0101] Result: Size of capsules: D[4,3]=146 μm. (This size is very
large, the reason being that, as seen in FIG. 6b, the capsules are
sticking together). FIG. 6b is a Scanning Electron Microscope image of
Example 6b.

EXAMPLE 6c

[0102] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing dimethylphthalate,
prepared with the high shear Ystral® (or Ultra Turrax®) process of
example 2.

[0103] A 10% w/w Suprasec® 5025, 45% w/w dimethylphthalate and 45% w/w
Solvesso®200ND solution was dispersed dropwise into a surface-modified
kaolin dispersion prepared according to Example 1, under high shear
mixing with an Ystral® high shear mixer at about 5000 rpm; and an O/W
emulsion was then prepared by high shear mixing with the Ystral® high
shear mixer at about 20000 rpm for 2 minutes. A 25% w/w
diethylenetriamine solution was then added to the emulsion under mixing
with the Ystral® high shear mixer at about 5000 rpm and an O/W
emulsion was then prepared by high shear mixing with the Ystral® high
shear mixer at about 20000 rpm for 2 minutes. The full composition is
identical to that given in Table 6b; the difference between Example 6b
and Example 6c lies in the preparation processes; ultrasonic and Ystral
processes respectively.

[0106] This Example illustrates the preparation of a Mowiol® 4-88
emulsion.

[0107] A 50% by weight solution of dimethyl phthalate in Solvesso®
200ND was dispersed dropwise into a 2% w/w solution of Mowiol® 4-88
(88% hydrolysed poly(vinyl acetate), MW ca. 28,000 Dalton), under high
shear mixing with an Ystral® high shear mixer. An O/W emulsion was
then prepared by high shear mixing with the Ystral® high shear mixer,
the speed of which was adjusted to yield a droplet size about 20 μm.
The full composition is given in Table 6d.

[0110] This Example provides release rate data for formulations prepared
according to Examples 6a to 6d.

[0111] Approximately 1 to 1.5 g of each of the four formulations described
in Examples 6a-6d was diluted by a factor of 10 into water. Each of these
solutions was placed in dialysis tubing and sealed in. Each dialysis tube
was placed in ca. 100 ml of water and was then left on rollers in a
temperature controlled room [temperature of 20(+/-2)° C.]. At
suitable intervals, the UV absorbance of the water phase was measured at
276 nm with a Perkin Elmer® UV spectrophotometer. This process allowed
the release of dimethylphthalate [DMP] into water to be followed with
time. Release curves shown below in FIG. 6e show that fast release was
seen for dimethyl phthalate from the PVA stabilized emulsion (Example 6d)
and from the unreacted clay stabilized emulsion (Example 6a). The rate of
release was greatly reduced when the clay had been reacted with
Suprasec® 5025 (Example 6b) or with diethylenetriamine (Example 6c).

EXAMPLE 7

[0112] This Example illustrates the preparation of a pre-dispersed
surface-modified clay slurry. 30 g of surface-modified clay particles (as
described in Example 1) were de-agglomerated (with a J&K mill) for 30
seconds prior to the addition of an equal weight of water. The slurry was
homogenised using a Flack-Tek dispersing unit for 30 seconds. The slurry
was later diluted with water to the desired concentration of 50% by
weight for use in the following Examples.

EXAMPLE 8

[0113] Examples 8, 9 and 10 illustrate the preparation of a single-layered
capsule suspension containing a pesticide, lambda-cyhalothrin dissolved
in Solvesso 200ND prepared with the high shear Ystral® process. A
Suprasec® 5025, lambda-cyhalothrin and Solvesso®200ND solution was
dispersed dropwise into a surface-modified kaolin dispersion prepared
according to Example 7, under high shear mixing with an Ystral® high
shear mixer at about 2000 rpm; and an O/W emulsion was then prepared by
high shear mixing with the Ystral® high shear mixer at about 2000 rpm
for 1 minute. A 25% w/w diethylenetriamine solution was then added to the
emulsion under mixing with the Ystral® high shear mixer at about 5000
rpm and an O/W emulsion was then prepared by high shear mixing with the
Ystral® high shear mixer at about 20000 rpm for 2 minutes. This
emulsion formed a single-layer capsule dispersion. The full composition
is given in Table 7.

[0114] Example 9 is an example of a capsule product containing both a
cross-linked bound clay particle and an extra polyurea binding layer. It
was prepared by taking the emulsion of Example 8 and treating it with
diethylenetriamine (cross-linker) in the quantities given in Table 8 and
mixing under low shear to homogenise the product

[0115] Example 10 is an example of a capsule product containing both a
cross-linked bound clay particle and an extra polyurethane binding layer.
It was prepared by taking the emulsion of Example 8 and treating it with
glycerol (cross-linker) and DABCO (catalyst) in the quantities given in
Table 9 and mixing under low shear to homogenise the product.

[0117] Examples 8, 9 and 10 immediately provided fluid dispersions that
did not change on overnight standing. Further cross-linking was effected
by heating the samples at 50° C. for 2 hours but the physical
characteristics of the products did not change.

[0118] To test the compatibility of these products with further added
components, an oil-in-water emulsion of a isoparaffinic oil (Isopar®
M) was prepared. Isopar M was dispersed dropwise into a 5% w/w solution
of Gohsenol® GL05 (88% hydrolysed poly(vinyl acetate)), under high
shear mixing with an Ystral® high shear mixer. An O/W emulsion was
then prepared by high shear mixing with the Ystral® high shear mixer,
the speed of which was adjusted to yield a droplet size about 10 μm.
The full composition is given in Table 10.

[0119] Equal volumes of samples of each of Examples 8, 9 and 10 were then
each independently mixed with an equal volume of the Isopar M emulsion.
All the samples remained fluid both immediately and after standing for 24
hours, demonstrating the compatibility of products of the invention with
an added oil-in-water emulsion.

EXAMPLE 11

[0120] This Example provides data on enhancement seen in the
photostability of lambda-cyhalothrin when trapped within Pickering
capsules.

EXAMPLE 11a

[0121] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing lambda cyhalothrin
prepared with the high shear Ystral® process. A 10% w/w Suprasec®
5025, 47.5% w/w lambda cyhalothrin and 47.5% w/w Solvesso®200ND
solution was dispersed dropwise into a surface-modified kaolin dispersion
prepared according to Example 7, under high shear mixing with an
Ystral® high shear mixer at about 5000 rpm; and an O/W emulsion was
then prepared by high shear mixing with the Ystral® high shear mixer
at about 20000 rpm for 2 minutes. This emulsion formed a single layer
capsule dispersion. A 25% w/w solution of diethylenetriamine (DETA) was
prepared in water and then this aqueous DETA solution was added dropwise
to the single-layered capsule suspension with mixing from an Ystral®
high shear mixer at about 5000 rpm. This capsule suspension was then
mixed by the Ystral® high shear mixer at about 20000 rpm for 2
minutes. The full composition is given in Table 11.

[0124] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing lambda cyhalothrin
prepared by the Ultrasonic process.

[0125] A 10% w/w Suprasec® 5025, 45% w/w lambda cyhalothrin and 45% w/w
Solvesso®200ND solution was dispersed dropwise into a surface-modified
kaolin dispersion prepared according to Example 7, under agitation with
an Ultrasonic Probe; and then an O/W emulsion was prepared by high shear
mixing with the Ultrasonic Probe for 2 minutes; under the following
conditions: 50% Duty cycle, Output Control 4. This emulsion formed a
single layer capsule dispersion. To this capsule suspension, a 25% w/w
diethylenetriamine solution was added under mixing with the Ultrasonic
Probe. The full composition is given below in Table 12.

[0127] Result: Size of capsules: D[4,3]=171 μm (this is large due to
aggregation of the capsules in the instrument, the electron micrograph
shows the capsule size to be smaller).

EXAMPLE 11c

[0128] Capsules according to Examples 11a and 11b were each assessed
against commercially available capsules [Karate Zeon®] in a
comparative study to determine the extent of protection provided by each
of the capsules to lambda-cyhalothrin against u.v. photodegradation.

[0129] For each capsule type, samples of microcapsules were spread on
glass slides and exposed to a xenon lamp (simulating sunlight) for up to
three days. Using standard techniques, the microcapsules were analysed to
determine the amount of lambda-cyhalothrin present in the formulations at
the initiation of exposure to ultraviolet light and the amount remaining
at various time periods during the three days' exposure.

[0130] The results are shown in FIG. 9. The capsules of the present
invention clearly provide better u.v. protection to lambda-cyhalothrin
than does the current commercial product.

EXAMPLE 12

[0131] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing dimethyl phthalate
(which is an example of a volatile organic molecule) prepared with the
high shear Ystral® process. A 10% w/w Suprasec® 5025, 47.5% w/w
dimethyl phthalate and 47.5% w/w Solvesso®200ND solution was dispersed
dropwise into a surface-modified kaolin dispersion prepared according to
Example 7, under high shear mixing with an Ystral® high shear mixer at
about 5000 rpm; and an O/W emulsion was then prepared by high shear
mixing with the Ystral® high shear mixer at about 20000 rpm for 2
minutes. This emulsion formed a single layer capsule dispersion. The
composition is given in Table 13.

[0132] A 25% w/w solution of diethylenetriamine (DETA) was prepared in
water and then varying amounts of this solution were added dropwise to
the single-layered capsule suspension with mixing from an Ystral® high
shear mixer at about 5000 rpm) to give a range of DETA concentrations
(0-1.3% by weight) in the final dispersions. Each capsule suspension was
then mixed by the Ystral® high shear mixer at about 20000 rpm for 2
minutes. The full composition is given in Table 14.

[0133] Approximately 1 to 1.5 g of each of these capsule formulations was
diluted by a factor of 10 into water. Each of these dilutions was placed
in dialysis tubing and sealed in. Each dialysis tube was placed in about
100 ml of water and was then left on rollers in a temperature controlled
room [temperature of 20(+/-2)° C.]. At suitable intervals, the LTV
absorbance of the water phase was measured at 276 nm with a Perkin
Elmer® UV spectrophotometer. This process allowed the release of
dimethylphthalate [DMP] into water to be followed with time; see FIG. 10,
which shows that increasing the DETA loading decreases the rate of
release of DMP from the capsules, showing that the rate of release is
readily controlled by the loading of DETA used in the formulation.

EXAMPLE 13

[0134] This Example illustrates the preparation of a single-layered
capsule suspension with diethylenetriamine containing mefenoxam prepared
with the high shear Ystral® process. The capsule dispersion was found
to show good redispersion properties after drying down to a dry deposit.
A 5% w/w Suprasec® 5025, 47.5% w/w mefenoxam and 47.5% w/w
Solvesso®200ND solution was dispersed dropwise into a surface-modified
kaolin dispersion prepared according to Example 7, under high shear
mixing with an Ystral® high shear mixer at about 5000 rpm; and an O/W
emulsion was then prepared by high shear mixing with the Ystral® high
shear mixer at about 20000 rpm for 2 minutes. This emulsion formed a
single layer capsule dispersion. A 25% w/w solution of diethylenetriamine
(DETA) was prepared in water and then this aqueous DETA solution was
added dropwise to the single-layered capsule suspension with mixing from
an Ystral® high shear mixer at about 5000 rpm. This capsule suspension
was then mixed by the Ystral® high shear mixer at about 20000 rpm for
2 minutes. The full composition is given in Table 15.

[0136] This formulation gave capsules that were stable on dry down, and
the capsules in the aqueous dispersion were stable over a period of 9
months at ambient temperature. A sample of this dispersion was allowed to
dry down in a plastic tray in a fume hood for 3 days, after which it was
found to redisperse readily in water with gentle agitation. FIG. 11 shows
the capsules in their original dispersion and FIG. 12 shows them in the
dispersion formed from the redispersion after dry down. The capsules
appeared to have lost some of the more volatile Solvesso® 200ND
through evaporation, but the capsules remained essentially intact and
showed facile redispersion.